A MOSFET has a gate electrode formed via a gate insulating film over a semiconductor substrate and source and drain regions formed in the semiconductor substrate on both sides of the gate electrode. Improvement in characteristics of such a MOSFET has been studied. Also, in order to achieve performance enhancement such as reduction of power consumption and higher speed of the semiconductor device having such a MOSFET, adoption of a SOI (Silicon On Insulator) substrate has been studied.
For example, Japanese Patent Application Laid-Open Publication No. 2001-284579 (Patent Document 1) discloses a technique for protecting a MOSFET from plasma by a protective diode. In addition, it discloses a technique for effectively protecting a MOSFET from plasma generated during the manufacture of the MOSFET by connecting a MOS capacitor having a dielectric breakdown voltage lower than that of the MOSFET to a gate of the MOSFET.